Light Ray Tracing Through a Leaf Cross Section

Abstract

A light ray, incident at about' 50 to the normal, is geometrically plotted through the drawing of the cross section of a soybean leaf using Fresnel's Equations and Snell's Law.The optical mediums of the leaf considered for ray tracing are: air, cell sap, chloroplast and cell wall. The above ray is also drawn through the same leaf cross section considering cell wall and air as the only optical mediums. The values of the reflection and transmission found from ray tracing agree closely with the experimental results obtained using a Beckman DK-2ASpe~troref1ectometer.

Optical Property Analyses of Plant Cells for Adaptive Optics Microscopy

“…This is also supported by the fact that leaves and shoot apical meristems, where cells contain chloroplasts, have more severe image degradation than roots, which lack chloroplasts. [21,22] The ellipsoidal shape and high refractive index of chloroplasts [25,32] indicate that they may serve as convex lenses to refract light. Also, we noticed that the phase contrast was inverted from white to black in chloroplasts (Figure 1(c), (e)), indicating that the mean phase of the rays through the chloroplasts was mostly inverted.…”

“…[21,22] Many epidermal cells with a planoconvex shape function as lens to focus light on chloroplasts in the subadjacent mesophyll cells, most likely to increase the efficiency of photosynthesis, and cylindrical rhizoid cells of bryophytes also refract light as lenses. [19,23,24] These lens effects appear to be caused by the plant cell wall; the cell wall has a refractive index of 1.41 À 1.52 in flowering plants, [20,[25][26][27] a value higher than the refractive indices of medium (n ¼ 1.33) and cytosol (n ¼ 1.35 À 1.39, estimated from that in animal cells). [28,29] These results indicate that the cell wall is expected to cause degradation in the images of living plant cells.…”

“…In addition, chloroplasts refract and scatter light. [30,31] The chloroplast stroma (the internal fluid of the chloroplast) has a refractive index of 1.42, [25,32] (stacks of photosynthetic membranes surrounded by the stroma) has higher pigment and protein contents, indicating that it likely has an even higher refractive index (n > 1.5). [28,29] These data suggest that chloroplasts likely also cause optical disturbances in imaging of live plant cells.…”

Satellite remote sensing of primary production

“…The interaction of incident solar radiation in the 0·4-2' 5J1m region with green leaves has been modelled using ray-tracing models (Allen et al 1973, Kumar andSilva 1973)and by a stochastic Markov-chain model (Tucker and Garrett 1977).To generate these models, scattering and absorption properties were required. Scattering by the structures within leaves has the effect of increasing the mean pathlength of the incident PAR, thereby allowing for high levels of PAR absorption by the photosynthetic pigments.…”

Leaf Optical Properties

“…Air-cell wall interfaces are probably the most important factors in determining leaf diffuse reflectance and transmittance; however, other interfaces or discontinuities as well as Rayleigh and Mie scattering may also contribute (Gausman 1974;Kumar and Silva 1973). The basic understanding of diffuse radiation is that each beam of light takes a unique path through the leaf tissue encountering different internal surfaces of varying geometric configurations and is reflected at each refractive index discontinuity (Kumar and Silva 1973;Gausman 1977).…”